Welding-type power supplies have become more sophisticated in recent years, including using digital communications, and having elaborate control schemes which are often at least partially digital. Welding-type power supplies with digital communication and control are particularly susceptible to EMI, which can more easily cause damage to the control and communication components. Welding-type power supply, as used herein, includes welding, heating or cutting power supplies.
Some prior art systems used a common mode inductance on the primary input lines, to block common mode noise. However, such prior art welding-type power supplies did not provide for protection from high frequency on the output studs. Indeed, there has not been a recognition in the prior art of the danger of noise coming back through the output cables, into the power supply.
EMI filtering typically includes shunting unwanted noise currents to the machine chassis or housing (by capacitors). However, this requires a low impedance between all sheet metal interfaces, or large voltages can develop which push unwanted noise currents into the signal lines. Such prior art EMI protection was adequate for welding-type power supplies that were not as sensitive as current systems with digital (or sensitive analog) components.
Unfortunately, prior art EMI protection is often not sufficient for modern systems, which can particularly fail from noise that enters the system from the output studs. Noise that can damage a welding-type power supply is often high frequency, such as in 2 to 20 MHz, or even in the hundreds of MHz range.
Accordingly, a welding-type power supply that is effectively protected from EMI or noise, particularly noise that is high frequency, such as 2 to 20 MHz, is desired.